In conventional power plants, consumers such as steam or gas turbines, are driven by live steam from the boiler. The mass flow is routed through the live steam line. The control of the mass steam flow takes place by interposed turbine control valves. The conventional rated speed of a pertinent turbine for producing a 50 Hz frequency is 3000 rpm. The pertinent speed has to be kept within a narrow percentage range. So-called quick-action valves, acting as servo valves which under certain prerequisites or criteria can undergo transition into so-called “quick-action”, are connected upstream of the actual turbine control valves. A specifiable criterion is, for example, coupling failure on the turbine shaft. This arrangement conventionally results in the turbine having a tendency to run in the direction of overspeed which can lead to its destruction. In this incipient case, in a very short available time interval, a safety circuit is triggered which blocks the mass flow upstream from the affected turbine, and thus, protects the turbine against overspeed and the concomitant damage.
In the known solutions, the so-called quick-action valves are generally hydraulically actuated, using an actuating device, generally in the form of a hydraulic cylinder (working cylinder). The hydraulic cylinder is equipped with plate springs. When the hydraulic cylinder is depressurized, under the action of the spring force, the piston rod of the cylinder extends in the process with the quick-action valve as the servo valve closing, and stops the mass flow supply to the turbine before it can reach the damaging overspeed range.
In the conventional safety circuits, as are used at present in turbine power plants, triggering of the working cylinder for actuating the respective quick-action valve of the turbine is implemented with solenoid valve concepts of simple structure. Malfunctions can relatively easily occur in the safety circuit, for example, when the actual switching function of the solenoid valve is disrupted by fouling or the like. Uncertainties in the safety circuit itself lead, of course, to uncertain conditions in the effective monitoring of the operating situation of the turbine. In the event of a process upset by failure of the safety circuit, major damage to the affected turbine can occur in the extreme case.